Shock, Horror and Blocks

Panic, Fear, Danger, Shock, Horror & Blocks.                                                          

In a heat of a real and imminent danger or hostile encounter,                  
with your body undergoing all sorts of extreme stress,
if all you can muster are basic Karate techniques from your available reaction toolbox /memory they should be;
 the Best ,  i.e. most effective and easy to use. 

Therefore, even if you only know a few solid practical Karate techniques let us say the bunkai of Pinan Katas for example, or whatever source, you should still be able to defend yourself, especially if you understand the principles and you have been practicing the fighting moves diligently. 
 (If you're thinking in terms of using sports applications, please, Don't !!!!)

*Understanding and practicing the actual depth of Pinan Kata and the Nai hanchi Kata will endow you with good fighting moves and skills.
(*Understanding is the key word here)

These basic Karate techniques are especially effective defensive street fighting moves trained properly AFTER you have:                                                          

 1. Distracted or blind sided your opponent, or caused him to lose focus on harming you.                                                                                  

 2. Moved away from his centre line, making it hard for him to reach or strike you.                                                                                                    

 3. Destroyed your opponent's limbs, balance, mobility, or vision.

Look at the so called "basic building block" techniques that it presumably teaches,      for good examples:   
                                                             

1. Gedan barai - as a downward forearm strike to your opponent's jaw line, back of arm, kidney or inner thigh. You can KO a person by striking 45 degree into his brachial plexus using this technique, especially after you have brought him down to his knees.  (Learn what this means) 

2. Jun-tsuki - as a straight punch to any of your opponent's "vital points" (not to totally pointless places) in while pulling him towards your punch simultaneously using Hikite.

3. Jodan (age) uke - as an upward forearm strike to your opponent's jaw line or neck while pulling him towards your forearm simultaneously using Hikite.

4. Shuto uke - as a scooping strike into the inner forearm of any incoming punch/grab/push/pull. This would weaken your opponent's arm and deflect it away to open up his neck for the returning knife-hand "to strike".

Similarly, "basic" Karate techniques like Soto uke and Uchi uke can be used to weaken or destroy the limbs and even knockout a person, when used as very violent street fighting moves. 
                Imagine these usages: (visualise practice and train)

5. Uchi uke - as a flurry of pulls, pushes and strikes to your opponent's upper chest, collar bone, neck and jaw. Hitting all these targets with one hand, like a solid club while unbalancing him violently with the other by grabbing his clothing. Or as a strike on the back of the arm, while you grab and pull his wrist towards you. These are very devastating  fighting moves because you strike your opponent repetitively like a frenzy while causing bewilderment to them by constant unbalancing. 

6. Shoto uke - as a whipping strike to the lower back of your opponent's head while pulling him towards you simultaneously using Hikite (withdrawing hand technique). The side of your arm would contact his neck, jaw or etc (initial damage) while your fist/hand would wrap around and hit the lower back of his head, possibly inducing a knockout. This is actually an advanced Karate technique. The more relaxed you are, the more damaging this or any whipping blow will be.

Simple and straightforward fighting moves that can be easily executed under stress;.   are the most useful tools in any personal armoury

SPEED and "Efficiency"  ARE THE MOST IMPORTANT ATTRIBUTES IN "BLOCKING"                                                                                            

To survive a real fight, you must be able to block “ i.e redirect”  the attacks on you and retaliate decisively preferable at the same time or premptively.
To be able to block successfully (in a blow for blow fashion) is insufficient by itself.  

To end a fight, you must hit him more and harder than he hit you. Practical  fighting techniques always consist of simple straightforward techniques emphasizing speed. With speed, you'll naturally get Efficiency & power.

For safety,
speed and efficiency,
most Karate "saving" techniques are both a block and strike. That means we hit our opponent at the same time "we block (i.e nullify) his strike" or nullify his intention to strike grab or injury by whatever means.

The first rule is: "Block and counterattack" must be one single movement.

1. Grab the opponent's striking limb and using hikite (withdrawing Hand technique), pull him towards you. (Many typical competition Karate styles teach hikite basically as a move to chamber a punch or block but never even use it in their competition training ....  something that's weird & illogical :-) ).               

 2. As you pull him towards you, strike his eyes, face, neck, throat or ribs hard, the choice of target depending on your last shifted position and your intention (stun, hurt or KO).